Light collection apparatus, system and method

ABSTRACT

An optical collector is disclosed which includes an imaging, aplanatic optical element having a front surface with a one-way light admitting portion, a back surface with a reflective portion, and an interior region of refractive material disposed between the front and backs surfaces.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and is a non-provisionalapplication of U.S. Provisional Patent Ser. No. 61/230,054 filed Jul.30, 2009, the disclosure of which is hereby incorporated by reference inits entirety for all purposes.

BACKGROUND

This disclosure relates to the concentration or collection of light,and, more particularly, the concentration or collection of light usingan optical element.

Typically, light concentrators operate to receive light incident over arange of angles less than an acceptance angle at an aperture. The lightis concentrated onto a region (e.g. on an absorber) with an area smallerthan the area of the aperture. The ratio of the aperture area to thesmaller area is known as the geometric concentration C. The laws ofthermodynamics set a theoretical upper bound, known in the art as the“thermodynamic limit,” to the concentration for a given concentratorconfiguration.

Many types of solar concentrators have been studied including reflectiveand refractive devices. Concentrators may be imaging or non-imaging, andmay be designed to correct for various types of optical aberration(spherical aberration, coma, astigmatism, chromatic aberration, etc.).For example, D. Lyndon-Bell, Monthly Notices of the Royal astronomicalSociety, vol. 334, pp. 787-796 (2002), describes an aplanaticconcentrator featuring primary and secondary reflectors. However, theefficiency of such concentrators is limited by the obscuration of theprimary reflector by the secondary reflector.

Optical concentrators may be applied, for example, in the conversion ofsolar energy to electricity (or other form of energy). The power that aphotovoltaic solar cell can produce is a function of the incidentsunlight. A typical solar cell can utilize efficiently many times theun-concentrated incident sunlight in typical settings, provided that thetemperature of the solar cell does not increase excessively. Therefore,an optical concentrator can be employed to concentrate sunlight onto aphotovoltaic cell to improve the output of the photovoltaic cell. Theoutput will increase with the concentration factor. At appreciableconcentration factors, cooling may be required, since the efficiency ofsome photovoltaic cells may decrease rapidly with increasingtemperatures.

Optical concentrators may be applied in a variety of other applicationsincluding, for example, imaging, photography, concentration of lightfrom sources such as lasers or light emitting diodes (LEDs), etc.

SUMMARY

The inventors have realized that a multiple surface optical concentratormay be used to concentrate light. At least one of the surfaces includesa one-way light admitting portion which selectively admits light throughthe surface into the concentrator while reflecting (e.g. via totalinternal reflection) light impinging on the surface from within theconcentrator. Such a concentrator may provide excellent concentrationwhile reducing or avoiding obscuration of further surfaces by thesurface which includes the one-way light admitting portion. In someembodiments, the concentrator may be an imaging aplanatic concentrator(i.e. substantially free of spherical and comatic aberration.) Suchconcentrators may be used in numerous applications including thecollection of solar energy.

The inventors have also realized that an imaging aplanatic multiplesurface optical concentrator of the type described herein may bedesigned using a flexible, convenient, and computationallystraightforward iterative method. Any number of techniques may then beused to manufacture the concentrator based on the design.

In one aspect, an apparatus for concentrating light from a source isdisclosed including: a front surface including a one-way light admittingportion; a back surface including a reflecting portion; and an internalregion disposed between the front surface and back surface. The one-waylight admitting portion admits at least a portion of light incident fromthe source from outside of the internal region into the internal regionand onto the reflecting portion of the back surface. The reflectingportion of the back surface reflects the portion of light back throughthe internal region towards the front surface facing the internalregion. The front surface includes a side facing the internal regionwhich reflects light incident from the back surface and concentrates thelight to a concentration region. At least a portion of the reflected andconcentrated light is reflected from the one-way light admitting portionof the front surface.

In some embodiments, the internal region includes a refractive material.In some embodiments, the refractive material includes dielectricmaterial.

In some embodiments, the one-way light admitting portion includes aninterface between the refractive material in the internal region and amaterial outside the internal region having a differing index ofrefraction, and where the portion of light reflected from the one-waylight admitting portion is reflected due to total internal reflection.

In some embodiments, the material outside the internal region having adiffering index of refraction has an index of refraction which is lessthat the index of refraction of the refractive material in the internalregion. In some embodiments, the material outside the internal regionincludes a fluid having an index of refraction of about n=1.

In some embodiments, the refractive material in the internal regionincludes a fluid.

In some embodiments, the refractive material includes a materialselected from the list consisting of: water, oil, mineral oil. Someembodiments further include a shell surrounding the internal region,where the shell may include the front and back surfaces. Someembodiments include a circulator for circulating the fluid through theinternal region. The circulator may be adapted to remove heat from theinternal region. Some embodiments include an absorber located proximalto the concentration region, and the circulator may be adapted to removeheat from the absorber. In some embodiments, the circulator includes aheat exchanger in thermal communication with the fluid and configured toremove heat from the fluid. Some embodiments include a heat converterwhich converts heat from the fluid to another form of energy.

In some embodiments, material outside the internal region includes afluid, e.g., water, oil, and/or mineral oil. Some embodiments include acirculator for circulating the fluid outside the internal region. Thecirculator may be adapted to remove heat from the internal region. Insome embodiments, the circulator includes a heat exchanger in thermalcommunication with the fluid and configured to remove heat from thefluid.

In some embodiments, the front surface, back surface, and internalregion are adapted to form an image of the source at the concentrationregion. In some embodiments, the front surface and back surface areaspherical surfaces adapted to substantially eliminate spherical andcomatic aberration of the image of the source. In some embodiments,light rays forming the image of the source substantially satisfy theAbbe sine condition.

In some embodiments, the reflecting portion of the back surface includesa metalized surface portion.

In some embodiments, the front surface includes a centrally locatedreflector including a reflective side facing towards the internal regionand a light blocking side facing away from the internal region. Theone-way light admitting portion of the front surface may substantiallysurround the centrally located reflector. In some embodiments, thecentrally located reflector provides a central obscuration of less thanabout 10%, 7%, 3%, or less.

In some embodiments, light from the source incident on the front surfaceat an angle of incidence less than about 2 degrees is concentrated tothe concentration region with an efficiency of greater than 70%, 80%,90% or more.

In some embodiments, light from the source incident on the front surfaceat an angle of incidence less than about 2 degrees is concentrated tothe concentration region with a geometrical concentration ratio of about500 or greater, 1,000 or greater, 1,200 or greater, 2000 or greater, oreven more.

In some embodiments, light from the source incident on the front surfaceat an angle of incidence less than about 1.5 degrees is concentrated tothe concentration region with a geometrical concentration ratio of about500 or greater, or 1,000 or greater, or 2,000 or greater.

In some embodiments, light from the source incident on the front surfaceat an angle of incidence less than about 1 degrees is concentrated tothe concentration region with a geometrical concentration ratio of about500 or greater, 1,000 or greater, 2,000 or greater, 3,000 or greater, or4,000 or greater.

In some embodiments, the source is imaged at an image plane in theconcentration region, and where the light forming the image of thesource is incident on the image plane at angles less than about 60degrees.

In some embodiments, light from the source incident on the front surfaceat an angle of incidence less than about 2 degrees is concentrated tothe concentration region at about the thermodynamic limit.

In some embodiments, the dielectric material includes at least onechosen from the group consisting of: glass, plastic, quartz, andtransparent fluid.

In some embodiments, the dielectric material has an index of refractiongreater than about 1.3.

Some embodiments further include the source. In some embodiments, thesource includes at least one chosen from the group consisting of: alight emitting diode; an organic light emitting diode, a laser; and alamp.

In another aspect, a system is disclosed including: an opticalconcentrator of the type described herein; and a light receiving elementlocated proximal to the concentration region. The optical concentratoris adapted to concentrate light from the source onto the energyabsorbing element.

In some embodiments, the light receiving element includes an energyconverting element adapted to absorb light concentrated at theconcentration region and output energy in response to the absorbedlight.

In some embodiments, the energy converting element outputs electricalenergy in response to the concentrated light.

In some embodiments, the light receiving element includes a photovoltaiccell.

In some embodiments, the energy converting element produces thermalenergy in response to the concentrated light.

In some embodiments, the light receiving element includes a photodiode,a laser gain medium, a photographic medium, or a digital imaging sensor.In some embodiments, the digital imaging sensor includes at least oneselection from the group consisting of: a CCD, a multi-pixel array ofphotodetectors, a CMOS detector. In some embodiments, the lightreceiving element includes a digital light processor or a MEMs device.

In another aspect, an optical imaging system is disclosed including aplurality of optical elements adapted to image light from an image planeonto an object plane, the plurality of lenses including the opticalconcentrator of the type described herein. In some embodiments, theplurality of optical elements include a telephoto lens system.

In another aspect, a method is disclosed for designing an imaging,aplanatic optical concentrator including a front surface with a one-waylight admitting portion, a back surface with a reflective portion, andan interior region of refractive material disposed therebetween, themethod including: determining the shape of the front and back surfacesby: defining an Abbe sphere with radius b; defining an initial rayparallel to an optical axis of the concentrator which is incident uponthe front surface at an initial front surface point located on the Abbesphere; selecting a position along the optical axis for an initial backsurface point; determining the surface tangent slope at each of theinitial front surface point and the initial back surface point byrequiring that light from the initial ray refracts at the initial frontsurface point, propagates along a propagation path through the interiorregion to the initial back surface point, reflects from the initial backsurface point, propagates back along the same propagation path to theinitial front surface point, reflects from the initial front surfacepoint due to total internal reflection, and propagates to the center ofthe Abbe sphere. The method further includes iteratively determining theposition and tangent slopes at additional front and back surfaces pointsbased on the positions of and surface tangent slopes at the initialfront and back surface points.

In some embodiments, determining the shape of the front and backsurfaces includes: determining cross sectional shapes of the front andback surfaces; and defining the shape of the front and back surfaces asthe rotation of the cross sectional shapes about the optical axis.

In some embodiments, the method includes defining a coordinate systemwith orthogonal axes Y and Z and intersecting at point P, where Zcorresponds to an optical axis of the concentrator; defining an Abbesphere with radius b centered at P; defining a series of N light raysRay #i, where i=0, 1, 2, . . . N−1, the rays traveling parallel to the Zaxis to intersect the front surface of the concentrator, and where A_(i)is a point where parallel Ray #i intersects the Abbe sphere; R_(i) is apoint where parallel Ray #i intersects front surface and refracts; B_(i)is a point where Ray #i intersects rear surface and reflects; X_(i) isthe point where Ray #i intersects front surface the second time andreflects; kB_(i) is the slope of the surface tangent at B_(i); andkX_(i): is the slope of the surface tangent at X_(i). The methodincludes selecting an angle θ; requiring that the (Y,Z) coordinates ofR₀ be (b cos(θ), b sin(θ)) such that R₀ lies in the Abbe sphere and A₀and X₀ coincide with R₀; selecting the Z coordinate of B₀; determiningk×₀ based on the relation k×₀=tan(a)=((n₀/n₁)+cos(θ))/sin(θ), where n₀is the index of refraction of a media surrounding the concentrator andn₁ is the index of refraction of the refractive material; determiningkB₀ based on the relation kB₀=(c tan(2α)c tan(θ)−1)/(c tan(θ)+ctan(2α)); constructing the front and back surfaces by iterativelydetermining X_(i) and B_(i) for i=1, 2, . . . , N−1. The iterativedetermination includes the steps of: determining X_(i+1) by extendingthe front surface along kX_(i) direction for a small step; determiningA_(i+1) as the intersection of the line from point P to point X_(i+1)with the Abbe sphere; determining R_(i+1) as the intersection of Ray#(i+1) passing through the Abbe sphere at A_(i+1) with the frontsurface; determining the path of propagation of light from Ray #(i+1)from point R_(i+1) through the interior region to the back surface;determining B_(i+1) by intersecting the path of propagation of lightfrom Ray #(i+1) from point R_(i+1) with a line extending along thekB_(n) direction; determining kB_(n+1) such that the ray of light fromR_(i+1) to B_(i+1) reflects at B_(i+1) back towards X_(n+1); determiningkX_(i+1) such that the ray of light from B_(i+1) to X_(i+1) reflects atX_(i+1) towards P.

Some embodiments include, for each point on the front surface, providingreflective material on the side of the front surface facing the interiorregion if the ray of light reflected from the back surface through theinterior region onto the point does not meet the condition for totalinternal reflection.

In another aspect, an optical concentrator is disclosed including: animaging, aplanatic optical element including a front surface with aone-way light admitting portion, a back surface with a reflectiveportion, and an internal region of refractive material disposed betweenthe front and backs surfaces. In some embodiments, the one way lightadmitting portion selectively admits light incident from outside theinternal region while reflecting light incident from the internalregion. In some embodiments, the one way light admitting portionreflects light incident from the internal region by total internalreflection.

In some embodiments, the optical element has an acceptance angle ofabout 2 degrees or greater. In some embodiments, the optical elementconcentrates light incident at less than the acceptance angle with aconcentration ratio of about 1000 or greater. In some embodiments, theoptical element concentrates light incident at less than the acceptanceangle with an efficiency of about 70% or greater. In some embodiments,the optical element concentrates light at about the thermodynamic limit.

In some embodiments, the internal region includes a refractive fluid.Some embodiments include a circulator configured to circulate therefractive fluid. In some embodiments, the optical element includes ashell defining the internal region, the shell including the front andback surfaces.

In another aspect, a method of concentrating light from a source isdisclosed including: providing a concentrator of the type disclosedherein; directing light from the source to the concentrator; and usingthe concentrator, concentrating light in the concentration region. Someembodiments include providing an absorber at the concentration region;and using the absorber, absorbing optical energy from the source. Someembodiments include converting absorbed optical energy into another formof energy.

In another aspect, an apparatus for collecting light from a source intoa beam of light, the apparatus including: a front surface including aselective light transmitting portion; a back surface including areflecting portion; and an internal region disposed between the frontsurface and back surface. The selectively light transmitting portionincludes a side facing the internal region which selectively reflectslight incident from the source back through the internal region towardsthe reflecting portion of the back surface. The reflecting portion ofthe back surface reflects the light from the front surface back throughthe internal region towards the front surface. The selectively lighttransmitting portion selectively transmitting at least a portion oflight incident from the reflecting portion of the back surface out ofthe internal region to form the beam of light.

In some embodiments, the internal region includes a refractive material.In some embodiments, the refractive material includes dielectricmaterial.

In some embodiments, the selectively light transmitting portion includesan interface between the refractive material in the internal region anda material outside the internal region having a differing index ofrefraction, and where the light selectively reflected from theselectively light transmitting portion is reflected due to totalinternal reflection. In some embodiments, the material outside theinternal region having a differing index of refraction has an index ofrefraction which is less that the index of refraction of the refractivematerial in the internal region. In some embodiments, the materialoutside the internal region includes a fluid having an index ofrefraction of about n=1.

In some embodiments, the refractive material in the internal regionincludes a fluid. In some embodiments, the refractive material includesa material selected from the list consisting of: water, oil, mineraloil. Some embodiments include a shell surrounding the internal region,the shell including the front and back surfaces. Some embodimentsinclude a circulator for circulating the fluid through the internalregion. In some embodiments, the circulator is adapted to remove heatfrom the internal region.

In some embodiments, the device includes a focal point located in afocal plane. The source is located proximal to the focal point, and thefront and back surfaces are configured to cooperate to collect lightfrom the source and substantially collimate the light into the beam.

In some embodiments, the front surface and back surface are asphericalsurfaces adapted to substantially eliminate spherical and comaticaberration associated with light collected from the source locatedproximal to the focal point.

In some embodiments, light rays collected from the focal point andcollimated into the beam substantially satisfy the Abbe sine condition.

In some embodiments, the reflecting portion of the back surface includesa metalized surface portion.

In some embodiments, the front surface includes a centrally locatedreflector including a reflective side facing towards the internal regionand a light blocking side facing away from the internal region. Theselectively light transmitting portion of the front surfacesubstantially surrounds the centrally located reflector. In someembodiments, the centrally located reflector provides a centralobscuration of less than about 3%, or less than about 7%, or less thanabout 10%.

In some embodiments, the apparatus is disposed about an optical axisextending normal to the focal plane, and where light emitted from thesource at angles less than 60 degrees from the optical axis, less than70 degrees, less than 80, degrees, less than 90 degrees, etc. arecollected into the beam. In some embodiments, at least 70%, at least80%, or at least 90% or more of the light energy or power emitted fromthe source is collected into the beam.

Some embodiments include the source. In some embodiments, the sourceincludes at least one chosen from the group consisting of: a lightemitting diode; an organic light emitting diode, a laser; a lamp.

In another aspect, a method is disclosed including: providing anapparatus for collecting light from a source into a beam of light, theapparatus including: a front surface including a selectively lighttransmitting portion, a back surface including a reflecting portionfacing the internal region; and an internal region disposed between thefront surface and back surface, the selectively light transmittingportion including a side facing the internal region. The method furtherincludes using the side selectively light transmitting portion facingthe internal region to selectively reflect light incident from thesource back through the internal region towards the reflecting portionof the back surface; using the reflecting portion of the back surface toreflect the light from the front surface back through the internalregion towards the front surface; and using the selectively lighttransmitting portion to selectively transmit at least a portion of lightincident from the reflecting portion of the back surface out of theinternal region to form the beam of light.

Some embodiments include directing the beam to illuminate a target. Insome embodiments, the source includes at least one chosen from the groupconsisting of: a light emitting diode; an organic light emitting diode;a laser; a lamp.

In various embodiments, the concentrators and collectors describedherein may be fast concentrators, e.g. having an f/number of 1.5 orless, 1 or less, 0.5 or less, 0.4 or less, or even faster. As usedherein, the f/number of an optical element is defined as one half timesthe inverse of the numerical aperture NA of the element. For an opticalelement having an acceptance angle θ, and working in a media having anindex of refraction n, the numerical aperture is given by NA=n sin θ.

Various embodiments may include any of the above described features,either alone, or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a perspective view of a concentrator.

FIG. 1B shows a cross section of the concentrator of FIG. 1A.

FIG. 2 is a ray trace diagram of the concentrator of FIG. 1A.

FIG. 2A is a ray trace diagram of a concentrator showing axial andoff-axial rays.

FIG. 2B is a perspective view of the concentrator shown in FIG. 2A.

FIG. 3A shows a two reflector concentrator of the type known in the art.

FIG. 3B shows a cross section of the concentrator of FIG. 1A.

FIG. 4 shows exemplary parameters for the concentrator of FIG. 1B.

FIG. 5 shows a plot of efficiency vs. incident angle for a concentrator.

FIG. 6 shows plots of intensity vs radial angle for a concentrator.

FIG. 7 shows exemplary performance parameters for concentrators havingvarious design parameters.

FIG. 8 shows a concentrator featuring a fluid filled internal region andcirculation system.

FIG. 9 shows a system featuring a concentrator with an absorber.

FIG. 10 shows a system featuring a light source and a concentrator.

FIG. 11 shows an optical system featuring a concentrator.

FIG. 12 shows a solar panel featuring a concentrator.

FIG. 13 shows solar energy collection system featuring a concentrator.

FIG. 14 is a flowchart illustrating steps for designing a concentrator.

FIG. 15 is a graphical ray illustration of the steps of FIG. 14.

FIG. 16 is an illuminator featuring a concentrator used in a lightcollection configuration.

DETAILED DESCRIPTION

FIG. 1A shows a perspective view of concentrator 100. FIG. 1B shows across section of concentrator 100 taken along diameter AA. Concentrator100 includes front surface 102 and back surface 104 positioned alongoptical axis Z. Surfaces 102 and 104 define an internal region 106containing a refractive material with index of refraction n.

Front surface 102 includes one way light admitting portion 108,described in greater detail below. Front surface 102 may optionallyinclude central reflector portion 110. Central reflector portion 110 isopaque to light impinging from outside of internal region 106 andreflective to light impinging from within internal region 106. Forexample, central reflector portion 110 may be a metalized mirror coatingon front surface 102.

Back surface 104 is reflective (e.g. having a metallized mirrorcoating). Light passing through front surface 102 and internal region106 onto back surface 104 is reflected back towards front surface 102.

Concentrator 100 operates to concentrate light incident on front surface102 to concentration region 112 located along optical axis Z at or nearback surface 104. An absorber 114 (e.g. a photovoltaic cell) mayoptionally be positioned at or near concentration region 112 to absorbconcentrated light. Concentrator 100 may optionally include cover glass116.

FIG. 1B shows a number of suitable exemplary dimensions for concentrator100. As shown, concentrator 100 has an outer diameter of 34.4 mm. Theminimum distance between front surface 102 and back surface 104 alongoptical axis Z is 6 mm while the maximum distance between the surfacesis 10 mm. Central reflecting portion 110 extends 5.5 mm radially fromoptical axis Z. It is to be understood that the above dimensions areexemplary in nature, and that any suitable dimensions may be used.

FIG. 2 is a ray trace diagram of concentrator 100 showing thepropagation of parallel rays 200 through the concentrator. A first groupof rays 200 propagate through collector 100 and are reflected from theinterior side of front surface 102 by total internal reflection (TIR)from one-way light admitting portion 108. For example, ray 200A isincident on front surface 102 at a point within one-way light admittingportion 108. One-way light admitting portion 108 is transparent to lightincident from outside of internal region 106. Accordingly, ray 200Apasses through front surface 102. At front surface 102, ray 200A isrefracted by the refractive material within internal region 106 anddirected towards a point on back surface 104. Ray 200A is reflected fromback surface 104 towards front surface 102 and towards optical axis Z.Ray 200A impinges point 202 on the interior side of front surface 102.The shapes of surfaces 102 and the refractive properties of the materialin internal region 106 are chosen to ensure that ray 200A meets thecondition for TIR at point 202. Accordingly, ray 200A reflects frompoint 200 and is directed back towards concentration region 112 locatedat or near back surface 104 near optical axis Z.

A second group of rays 200 propagate through collector 100 and arereflected from the interior side of front surface 102 by reflectorportion 110 instead of by TIR from one-way light admitting portion 108.For example, ray 200B is incident on front surface 102 at a point withinone-way light admitting portion 108. Ray 200B passes through frontsurface 102, is refracted by the refractive material within internalregion 106 and directed towards a point on back surface 104. Ray 200B isreflected from back surface 104 towards front surface 102 and towardsoptical axis Z. Ray 200A impinges point 204 on the interior side offront surface 102 within central reflector portion 110. Centralreflector portion 110 includes a reflective surface (e.g. a metalizedmirror surface) on the interior side of front surface 102 which reflectsray 200B back towards concentration region 112 located at or near backsurface 104 near optical axis Z.

A third group of rays, for example ray 200C, are incident on frontsurface 102 within central reflector portion 110. Such rays are blockedby central reflector portion 110, creating central obscuration 206. Notehowever, that central obscuration 206 is small compared to the remainderof front surface 102, such that the vast majority of light incident onsurface 102 passes into the concentrator to be concentrated to region112. For example, in some embodiments the central obscuration may beabout 3% or less.

As shown, concentrator 100 provides aplanatic imaging. Concentrator 100forms an image of a light source at region 112 which is free fromcomatic aberration. In other words, concentrator 100 obeys the wellknown Abbe sine condition. For example, for a source located at“infinity”, the sine condition requires that each ray incident from thesource in the direction parallel to the optical axis of the concentratorintersects its conjugate ray on a sphere having a radius equal to thefocal length of the concentrator and centered at the focal point(referred to as the “Abbe sphere”).

FIG. 2A shows a ray trace of diagram of the propagation of parallel rays200 and off-axial rays 200D through the concentrator 100. Off axial rays200D are incident at on concentrator 100 at an angle of 2 degrees fromparallel with the optical axis. As shown, the rays that would have hitthe central obscuration 206 are blocked by a screen for illustrationpurpose. Also shown in inset is a close-up on the concentration region116, where sharp focusing of both on-axial and off-axial rays indicatesthe aplanatic nature of the design.

As shown in FIG. 2A, concentrator 100 has an angular aperture of 60degrees (0=60 degree), indicative of a very fast system. The sharpfocusing of both on-axial and off-axial (2 degree) rays indicates theaplanatic nature of the design. The central reflector portion 110 iscoated with reflective material, but the obscuration of the input lightis only less than 4%. In other words, most area of the front surfaceacts as a “one-way” mirror, as described above. In the embodiment shown,the aspect (height: diameter) of this aplanat is approximately 1:3.

FIG. 2B is a perspective view of the concentrator shown in FIG. 2A

FIG. 3A shows a prior art two surface imaging aplanatic concentrator 300of the type described in D. Lyndon-Bell, Monthly Notices of the royalastronomical society, vol. 334, pp. 787-796 (2002). Concentrator 300includes primary reflector and secondary reflector 304. Light incidenton primary reflector 302 through opening 306 is reflected back ontosecondary reflector 304 and concentrated at region 308. Theconcentration obtained by concentrator 300 tends to increase with anincrease in size of secondary reflector 304. However, secondaryreflector 304 acts to obscure primary reflector 302 (i.e. by reducingthe size of opening 306). Thus, increasing the size of secondaryreflector 304 results in an unavoidable trade off between (unwanted)central obscuration and (desired) concentration.

Referring to FIG. 3B, concentrator 100 does not suffer from the abovedescribed trade off. Substantially all of the interior side of frontsurface 102 is available to reflect light incident from back surface 104(either from central reflection portion 110 or one-way light admittingportion 108). However, as noted above, because one-way light admittingportion 108 is transparent to light impinging on the outer-facing sideof front surface 102, collector 100 suffers only from a small centralobscuration 206 caused by central reflector portion 110. Accordingly,collector 100 provides good performance and flexibility of design.

FIG. 4 shows exemplary parameters for a concentrator of the time shownin FIG. 1B with a concentrator diameter of about 34 mm, thickness ofabout 10 mm, and index of refraction n of about 1.52. Such concentratormay provide geometrical concentration C=1,200 or greater, near thethermodynamic limit. The optical efficiency may be 87% or greater withno cover glass, and 79% or greater with a cover glass. In this example,the reflectivity of back surface 102 is about 95%, and the centralobscuration 206 about 3%.

The acceptance angle of the concentrator may be +/−2 degrees or greater.For example, FIG. 5 shows an exemplary plot of optical efficiency vs.incident angle for concentrator 100 with no cover glass. As shown,optical efficiency may be high and nearly constant for acceptance anglesof +/−2 degrees or more.

Still referring to the example of FIG. 4, absorber 114 was aphotovoltaic cell with a radius of about 1 mm. In typical applications,such a cell can only effectively convert light incident at an angle lessthan a maximum cell acceptance angle. In the current example,concentrator 100 concentrates, substantially, light on the cell atangles of incidence less than about 60 degrees. For example, FIG. 6shows exemplary plots 600A and 600B of the intensity of encircled energyincident on the cell vs. the radial angle (i.e. angle of incidence).Plot 600A refers to source light striking concentrator 100 at normalincidence while plot 600B refers to source light striking concentrator100 at 2 degrees off axis. As indicated by the sharp inflection points602A and 602B in plots 600A and 600B, substantially all of the lightstriking the cell may do so at angles less than 60 degrees.

Although specific exemplary parameters are given above, it is to beunderstood that other configurations may be used and even tailored to aparticular application. For example, FIG. 7 shows exemplary performancecharacteristics for a variety of possible configurations of concentrator100, each having index of refraction n of about 1.52. For example, for aconcentrator with an acceptance angle of about +/−1 degree, ageometrical concentration C up to about 4,100 or greater may beprovided. For a concentrator with an acceptance angle of about +/−1.5degrees, a geometrical concentration C up to about 2,048 or greater maybe provided. For a concentrator with an acceptance angle of about +/−2degrees, a geometrical concentration C up to about 1,200 or greater maybe provided. For a concentrator with an acceptance angle of about +/−2.5degrees, a geometrical concentration C up to about 770 or greater may beprovided. Note, in each case the available concentration comparesfavorably with the theoretical maximum.

If one considers the image generated by concentrator 100 as pixels atthe focal plane, an important property is the amount of light on eachpixel. This is called the speed of the optical system and is related tothe angular cone of light on the pixel; the larger the angle, the fasterthe system. In various embodiments, the concentrators described hereinmay be highly compact and fast aplanatic singlets. In some embodiments,the f/number (defined as the ratio of the focal length of theconcentrator divided by the diameter of the entrance pupil) isapproximately 1, 0.5, 0.4 or less, while the aspect (height: diameter)of this aplanat is approximately 1:1, 1:2, 1:3 or even less.

In various embodiments, concentrator 100 may be constructed of anysuitable materials. For example, concentrator 100 may be formed fromrefractive material such as glass, plastic, quartz, etc. The materialmay include any suitable type of material including dielectrics,semiconductors, non linear optical (NLO) materials, active gain media,graded index of refraction (GRIN) materials, photonic crystals,nano-structured materials, etc.

Referring to FIG. 8, in some embodiments, concentrator 100 may include ashell 801 formed from surfaces 102 and 104. Internal region 106 is atleast partially filled with a refractive fluid 800 (indicated with wavylines). The fluid may be, for example, a liquid (e.g. water or mineraloil), gas, gel, or a mixture thereof. Shell 801 may be formed of anysuitable material, e.g. plastic, glass, quartz, etc. In someembodiments, the fluid 800 may have an index of refraction which issubstantially the same as that of shell 801. In other embodiments, theindices of refraction may differ.

Fluid 800 may be circulated (as indicated by broad arrows) throughinternal region 106 using pump 802. This circulation may operate toremove unwanted heat generated by the concentration of light ontoabsorber 114. Fluid 800 may also flow through heat exchanger 804 forcooling. In various embodiments, heat exchanger 804 may convert heatenergy from fluid 800 into other forms of energy, e.g. electricity,using any suitable technique. Pump 802 and heat exchanger 804 maycommunicate with one or more sensors (not shown) either internal to orexternal from concentrator 100 in order to maintain the temperature ofthe concentrator within an acceptable temperature range (e.g. thepreferred operating range of absorber 114). Note that although a closedcirculation system is shown, other suitable types of fluid flow systemsmay be used.

In some embodiments, concentrator 100 may be situated in an externalfluid medium. This medium may be circulated using techniques similar tothose described above to remove heat from concentrator 100 or partsthereof. In various embodiments, this heat may be converted to othertypes of energy using any suitable technique.

Referring to FIG. 9, concentrator 100 concentrates light from a source(not shown) onto absorber 114. Absorber 114 converts energy from theincident light into another form, and transmits this energy to module900. Module 900 may, e.g., store the energy, use the energy to perform afunction, further convert the energy, and/or transmit the energy toanother location. For example, as noted above, absorber 114 may be aphotovoltaic cell which converts solar energy to electrical energy (i.e.by producing a current or voltage). In some embodiments, thephotovoltaic cell may be a high efficiency multi junction cell.

However, absorber 114 may take any suitable form including, for example:a photo cell, a photodetector, photodiode, a charge coupled device, amulti-pixel array of photodetectors, a CMOS detector, a scintillator, adigital camera, a digital light projector, a recording media such asphotographic film, a photo-sensitive chemical, a thermocouple, aheatable thermal mass, a MEMs device, a laser gain media, etc.

Note that although FIG. 9 graphically represents the link betweenabsorber 114 and module 900 with a wire, any suitable link may be used.For example, energy may be transmitted wirelessly from absorber 114 tomodule 900 in the form of inductive coupling, a laser or other lightbeam, RF energy, microwave energy, etc. The link may be a directphysical link. For example, absorber 114 may convert light energy toheat to boil water and transmit energy to module 900 via a steam pipesystem or similar techniques.

In some embodiments, the shape of the distribution of light concentratedby concentrator 100 may fail to match the shape of the operating surfaceof absorber 114. For example, absorber 114 may be a square shapedphotocell while concentrator 100 may concentrate solar light to acircular spot, leading to inefficiency in absorption/conversion of solarenergy. To correct such mismatch, in some embodiments one or moreoptical elements may be used to adjust the distribution of concentratedlight produced by concentrator 100 at absorber 114.

Referring to FIG. 10, concentrator 100 concentrates light from source902 to region 100 onto absorber 114 located on or near concentrationregion 112. For example, source 902 may be a light emitting diode andabsorber 114 a diode pumped laser gain medium. In such a case,concentrator 100 may operate to concentrate light from the lightemitting diode onto the gain medium to achieve efficient pumping of thelaser. As will be understood by those skilled in the art, any of avariety of light sources may benefit from concentration of output lightby concentrator 100. Such sources include: light emitting diodes,organic light emitting diodes, lasers (e.g. diode lasers), lamps(incandescent, fluorescent, etc.), fluorescent or phosphorescentmaterials, amplified stimulated emission sources, etc.

In various embodiments, concentrator 100 may be included in an opticalsystem with one or more other optical elements (refractive, reflective,or otherwise). For example, FIG. 11 shows a telephoto lens 1100 whichincludes an aperture 1102, telephoto lens group and concentrator 100arranged along an optical axis. In various embodiments lens 1100 mayinclude additional optical elements, aperture stops, and so forth (notshown). Concentrator 100 may operate to image and concentrate light fromlens group 1104 onto photographic media 1106. Such concentration mayprovide for very fast exposure photographic media 1106. Concentrator 100may similarly be employed in any number of other optical applicationsincluding, for example, microscopy, photolithography, telescopes (e.g.for astronomical observation, etc.)

Referring to FIG. 12, in one embodiment, solar panel 1200 includes anarray 1202 of concentrators 100 of the type described herein. Eachconcentrator 100 concentrates sunlight onto an absorber 114 (e.g. aphotovoltaic cell or thermal cell) which in turn converts theconcentrated solar energy into another form (e.g. electrical or thermalenergy). Panel 1200 may include one or more connections betweenabsorbers 114 for collecting the converted energy and directing it tooutput 1204. Note that although, as shown, panel 1200 features a flatregular, two dimensional array of collectors 100, in various embodimentsother configurations may be used, including, for example one or threedimensional arrays, irregular patterns in any number of dimensions,curved arrays, etc.

Referring to FIG. 13, in one embodiment, solar energy collector 1300moves solar panel 1200 to track the movement of the sun 1301 across thesky in order to maximize the energy obtained (e.g. by maximizing thelight incident on collectors 100 at angles less than the associatedacceptance angle). Controller 1302 controls motorized mount 1304 to movepanel 1200 along one or more degrees of freedom. Controller 1302 maymonitor the output of panel 1200, thereby providing a feedback mechanismfor positioning the panel. Of course it is to be understood that asimilar collector system could be employed to track other (non-solar)light sources.

The above described devices and systems may be designed and manufacturedusing any suitable technique known in the art. The following describesexemplary convenient methods for concentrator design and construction.

In general, an imaging, aplanatic (i.e. substantially obeying the Abbesine condition) may be easily designed using a “seed ray” approach. AnAbbe sphere is defined for the concentrator along an optical axis. Aseed ray parallel to the optical axis is defined which intersects thefront surface of the concentrator on the Abbe sphere. The seed rayrefracts from the front surface, propagates to the back surface, whereit is required to retroreflect back along its path towards the frontsurface. The retroreflector ray strikes the front surface again at thesame point on the Abbe sphere and is reflected by TIR (or anotherprocess) and directed towards the center of the Abbe sphere. Based onthe above conditions, and on the index of refraction of the concentratorand the media in which it is situated, the positions and surfacetangents of points on the front and back surfaces may be obtained. Thisinformation may then be utilized to iteratively determine the totalshapes of the front and back surfaces.

For example, Referring to FIG. 14, process 1400 may be used to determinethe shapes of front and back surfaces 102 and 104 of an imaging,aplanatic embodiment of concentrator 100. In the interest of clarity,FIG. 15 provides an exemplary graphical representation of process 1400.Initially, assume that the concentrator lies along an optical axis Z,and is composed of a material with index of refraction n₁ and issituated in a medium (e.g. air) having index of refraction n₀. Asexplained in detail below, process 1400 traces a number of rays parallelto the optical axis and incident on concentrator 100 to iterativelydetermine the shapes of front surface 102 and back surface 104 ofconcentrator 100 (as they lie in a Y-Z plane arranged along a diameterof the concentrator). In the following discussion, define the variablesbelow, where the index i runs over 0, 1, 2, 3 . . . , N. The upper limitN may be chosen based on design requirements (i.e. a larger N willprovide a finer design surface output, but will make the iterativeprocess more computationally expensive).

P: the center of an Abbe Sphere of radius b, also is the origin of theY-Z coordinate system shown in FIG. 15;

A_(i): the point where parallel Ray #i intersects the Abbe sphere;

R_(i): the point where parallel Ray #i intersects front surface andrefracts;

B_(i): the point where Ray #i intersects rear surface and reflects;

X_(i): the point where Ray #i intersects front surface 102 the secondtime and reflects (by TIR or mirror);

kB_(i): the slope of the surface tangent at B_(i);

kX_(i): the slope of the surface tangent at X_(i).

In step 1402 of process 1400, define an Abbe sphere of radius b equal tothe focal length of the concentrator. The Abbe sphere is centered at thefocal point of the concentrator. In step 1404 define a parallel “seed”ray (Ray #0).

In step 1406 intersect the seed Ray #0 with the front surface at pointA₀ on the Abbe sphere. As shown in FIG. 15, this may be accomplished bychoosing an angle θ and letting the (Y,Z) coordinates of point R₀, whereseed Ray #0 intersects front surface 102 and refracts, be (−b cos(θ), bsin(θ)), such that R₀ lies in the Abbe sphere. Then A₀ and X₀ mustnecessarily coincide with R₀.

In step 1408, choose the Z position along the optical axis by choosingthe Z coordinate Z₂ of B₀. In step 1410, propagate Ray #0 (i.e., basedon Snell's law and the principals of ray optics) from A₀ to intersectwith the back surface. In step 1412, determine the Y coordinate of pointB₀ where Ray #) intersects rear surface and reflects. In step 1414,require that the seed ray retroreflects from the back surface towardsthe front surface. In step 1416, determine kB₀, the slope of the surfacetangent at B₀. For example, in terms of the angles shown in FIG. 15,kB₀=tan(β)=(c tan(2α)c tan(θ)−1)/(c tan(θ)+c tan(2α)).

In step 1418, propagate the seed ray back to the front surface and, instep 1420, require total internal reflection of the seed ray from thefront surface toward P the center of the Abbe sphere. Based on thisrequirement, in step 1422 determine X₀ the slope of the surface tangentat X₀. For example, in terms of the angles shown in FIG. 15,k×₀=tan(α)=((n₀/n₁)+cos(θ))/sin(θ).

In step 1424, based on X₀, B₀, and k×₀, kB₀, extend the front and backsurfaces at points X₀, B₀ a small distance along the surface tangents.In step 1426, propagate N additional parallel rays to iterativelydetermine the complete shapes of the front and back surface. Forexample, in a first iteration:

a. Determine X_(n+1) by extending the front surface along kX_(n)direction for a small step;

b. Determine An₊₁ by intersecting line PX_(n+1) with the Abbe sphere;

c. Determine R_(n+1) by interesting Ray #(n+1) with the front surface;

d. Using Snell Law to determine Ray R_(n+1)B_(n+1);

e. Determine B_(n+1) by intersecting Ray R_(n+1)B_(n+1) with theextension of the rear surface along the kB_(n) direction;

f. Determine KB_(n+1) such that Ray R_(n+1)B_(n+1) reflects back towardsX_(n+1);

g. Determine kX_(n+1) such that Ray B_(n+1)X_(n+1) reflects towards P;

These steps may then be repeated until the whole surfaces areconstructed. Once the complete surfaces are determines in the Y-Z plane,they may be rotated about the optical Z axis to provide a complete threedimensional shape for the concentrator.

Note that the above process provides a number of free parameters (e.g.,b, θ, Z₂). This provides a great deal of flexibility in choice of designparameters. Further, the process is straightforward and notcomputationally intensive. For example, Table 1 contains a simpleexemplary script for implementing a process of the type described abovein the well known Scilab scientific computing environment (available at“http://www.scilab.org”).

TABLE 1 Exemplary Script//*********************************************************************************************************************************************** //******** This program is to construct a TIRaplanatic CPV according to the algorithm developed by UCM group.//******** The construction is simply on a 2D surface (XY plane) due torotational symmetry. //******** The convention used in the codes for thetwo constructed surfaces are as following: //******** (Xc3, Rc3) and kc3are the XY coordinates and the slope of the front surface (corrector),respectively; //******** (Xp3, Rp3) and kp3 are the XY coordinates andthe slope of the back surface (primary mirror), respectively. //********Users can assign values to the following two free parameters://********  (1) u: initial separation of the front and back surfacealong the X direction; //********  (2) phim: maximum acceptance anglethat the cell can take. //******** The resolution of the built surfacesis controlled by NumProfile (default is 1000), which specifies how densethe surfaces would be sampled. //******** The result is plotted as agraph by default (pfile=0), user can choose to also output the resultsto a txt file by letting pfile=1. //********----------------------------------------------------------------------------------------------------------------------- -//********************************************************************************************************************************************** // Display mode mode(0); // Display warning forfloating point exception ieee(1); //****** define functions *********//given two lines (y−y1)=k1*(x−x1), (y−y2)=k2*(x−x2), return the crosspoint of the two lines (x3,y3) function[x3,y3]=linecross(x1,y1,k1,x2,y2,k2)  x3=−(−y2+y1+k2*x2−k1*x1)/(k1−k2); y3=−(k1*(k2*x2−y2)+k2*y1−k1*k2*x1)/(k1−k2); endfunction //given twopoints (x1,y1),(x2,y2), return slope k of the line that connects the twopoints function [k]=slope2p(x1,y1,x2,y2)  k=(y2−y1)/(x2−x1); endfunction//given two points (x1,y1),(x2,y2), return the slope k of the lineperpendicular to the line that connects the two points function[k]=nslope2p(x1,y1,x2,y2)  k=−(x2−x1)/(y2−y1); endfunction //given theslope k1,k2 of two rays, return the slope km of a mirror that reflectsone ray to the other function [km]=mirrorslope10(k1,k2)  alfa1=atan(k1); alfa2=atan(k2);  bia=alfa2−alfa1;  km=tan(alfa1+bia/2+%pi/2);endfunction //******* end of define functions ******** // *** programcontrol variables ***// pfile=0; //weather to print the results to a txtfile. 0:no, 1:yes NumProfile = 1000; //how many points on theconstructed surfaces // *** end of control variables ***// //*****constants ******** n0=1;  //refractive index of airn1=1.5249; //refractive index of Schott BK270 at 550 nm b=1;   // radiusof Abbe sphere // ***** end of constants ***** // ****** free parameters******* u=b*0.0065; // u: initial separation of the front and backsurface along the X direction phim=61/180*%pi; // maximum acceptanceangle v=b*cos(phim); // v: front surface initial displacement along Xdirection // ***** end of free parameters ****** //***** increment ofeach step in y direction *****// phiMin=1e−20; phiMax=phim;SinPhiMin=sin(phiMin);SinPhiMax=sin(phiMax);SinPhiStep=(SinPhiMax−SinPhiMin)/NumProfile; // *** the starting pointsand the initial slope of both surfaces  ka=(n0/n1+cos(phim))/sin(phim); alfa=atan(ka);  ku=tan(2*alfa+phim−%pi/2);  Xc3(NumProfile)=−v; Rc3(NumProfile)=SinPhiMax;  Xp3(NumProfile)=Xc3(NumProfile)+u; Rp3(NumProfile)=SinPhiMax−u/ku;  kc3(NumProfile)=ka; kp3(NumProfile)=ku; // iterates to construct the new portions fori=(NumProfile−1):−1:1  hhh=SinPhiMin+(i)*SinPhiStep; //y coord of thenew front portion //coords of the new front portion [Xc3(i),Rc3(i)]=linecross(Xc3(i+1),Rc3(i+1),kc3(i+1),0,hhh,0); //Abbeangle  phi=−atan(Rc3(i)/Xc3(i)); //height of Abbe ray  h=b*sin(phi);//find the place where the Abbe ray interacts the front surface  forj=NumProfile:−1:i   if h>Rc3(j) then hpl=j; break; end;  end; auxs=kc3(hpl+1);  hx=Xc3(hpl+1)+(h−Rc3(hpl+1))/auxs; // x coord, y is h// refraction on the front surface, determine the slope of the refractedray  auxs=−1/kc3(hpl+1);  alfai=atan(auxs);//incident angle alfao=asin(n0*sin(alfai)/n1); // refraction angle kRefractedRay=tan(atan(auxs)−alfao); //slope of the refracted ray //coord of the new back portion is determined by extending the existingportion (slope) and then intersecting with the refracted ray[Xp3(i),Rp3(i)]=linecross(hx,h,kRefractedRay,Xp3(i+1),Rp3(i+1),kp3(i+1)); // Determine the slope of the back portion and the frontportion  klink=slope2p(Xc3(i),Rc3(i),Xp3(i),Rp3(i));//klink is the slopeof the line connects the two points [kp3(i)]=mirrorslope10(kRefractedRay,klink); [kc3(i)]=mirrorslope10(−tan(phi),klink); end //*********** plot theprofiles******************* plot(Xc3, Rc3, Xp3,Rp3); set(gca(),“isoview”,“on”); mtlb_grid; //***********output to a txt file*********************** if pfile==1 then  BacksurfaceShift=0.2;//**********accomodate to lightool lens spline sweep u=file(‘open’,‘.\result.txt’,‘unknown’); fprintf(u,‘%f,%f,%f,%f\n’,0,−Xc3(1),0,Xp3(1)−BacksurfaceShift);  fori=1:(NumProfile/500):NumProfile fprintf(u,‘%f,%f,%f,%f\n’,Rc3(i),−Xc3(i),Rp3(i),Xp3(i)−BacksurfaceShift);  end;  i=NumProfile; fprintf(u,‘%f,%f,%f,%f\n’,Rc3(i),−Xc3(i),Rp3(i),Xp3(i)−BacksurfaceShift);  file(‘close’,u); end;

It is to be understood that, while the above described design method maybe employed in some embodiments to design concentrators (or equivalentcollectors, as described below) of the type described herein, otherdesigns methods may be used. For example, in some embodiments, an edgeray approach may be used, in which both edges of the image formed by theconcentrator is required to be bound by rays from opposite edges of thesource (i.e., incoming rays at the edges of the input pupil of theconcentrator incident at angles corresponding to the acceptance.) Ageneral treatment of edge ray design techniques may be found, e.g., inRoland Winston et al, Nonimaging Optics, Academic Press (Elsevier) 2005.In typical embodiments, such edge ray techniques do not result in aperfectly aplanatic device, but instead present a trade off betweenacceptance angle and spot size at the image plane. However, in manycases, for relatively small acceptance angles (e.g., less than 5.0degrees, less than 2.5 degrees, less than 1.0 degrees, less than 0.5degrees, or smaller), the spot size increases only slowly (e.g.,quadratically) as a function of acceptance angle. Accordingly, for mayapplications, the edge ray design may result in a concentrator having asuitable acceptance angle while suffering from only slight sphericalaberration.

Any suitable manufacturing technique may be employed to manufactureconcentrators based on designs produced using the above describedtechniques. For example, process 1400 may output the concentrator designin the form of computer instructions to be implemented on one or moreautomated manufacturing devices.

It is to be understood that the above described devices may include anysuitable materials. Surfaces of concentrator 100 may include anysuitable optical coating (e.g. anti-reflective coating) or othertreatment. Although one-way light admitting surface portions whichemploy TIR have been described, any other suitable techniques known inthe art may be employed to selectively provide one-way light admission.

Also disclosed herein is a method of concentrating light using aconcentrator of the type disclosed herein. In various embodimentsinclude directing light from a source onto the concentrator to beconcentrated in a concentration region. An absorber may be positioned inor near the concentration region to absorb concentrated light. Theabsorber may be used to convert the concentrated light energy to anotherform of energy, e.g. electrical, thermal, chemical, or mechanicalenergy. Various embodiment may include cooling the concentrator orabsorber, e.g., by circulation of fluid.

Although the above examples have shown a concentrator 100 which operatesto receive light from a source incident on the front surface andconcentrate the light to a concentration region, it is to be understoodthat the same device may also be used “in reverse” to collect light fromsource located at the concentration region and form a collimated beamfrom the collected light which is output from the front surface. Forexample, referring to FIG. 16, concentrator 100 is employed as a lightcollector. A light source 1600 (e.g. an LED, OLED, laser, lamp,filament, infrared source, etc.) is located at or near the focal pointin the focal plane of the concentrator 100. As illustrated by rays 200,light from source 1600 is collected from the source and collimated toform beam 1601. Beam 1601 is output from front surface 102. Beam 1601may be directed (directly or using any suitable optical elements) to atarget (not shown) to provide illumination. In some embodiments, severalsource/collector devices may be used, e.g. arranged in an array toprovide a combined output beam.

Various embodiments of concentrator 100, when used in the abovedescribed collector configuration, may have any of the opticalcharacteristics of concentrators described herein. For example, in someembodiments, the concentrator can be imaging and aplanatic, as describedabove. In some embodiments, the collector can operate to collectsubstantially all of the light emitted from the source at angles rangingfrom 0 to 30 degrees, 0 to 40 degrees, 0 to 50 degrees, or even 0 to 60degrees or greater from the optical axis. In various embodiments, atleast 50%, 60%, 70%, 80%, or even more of the light energy or power(i.e., energy per unit time) emitted from the source is collected intothe beam.

As will be understood by one skilled in the art, a collector of thistype may be used advantageously in any application where efficientcollection of light into a well collimated beam is desired. For example,in some embodiments, the collector may be used in a flashlight tocollect light from an led source into an intense, well collimated beam.One or more collectors of this type may be used in other types ofillumination devices including, for example, illuminated signs, trafficsignals, lighting fixtures, etc. One or more collectors of this type maybe included in any know detector device or system which employs acollimated beam, including, for example a position or motion detector(e.g. as used for range finding, security applications, speed detection,etc.) One or more collectors of this type may be included in any knowoptical communication device or system, e.g., an optical switch. In someembodiments, the output beam of the collector may be coupled into anoptical fiber, wave guide, etc.

In some embodiments, a method may include the step of providing a devicefor collecting light from a source into a beam of light (e.g.,concentrator 100, operating in the collector configuration, henceforth a“collector”). As described in detail above, in some embodiments,collector 100 includes a front surface including a selectively lighttransmitting portion, a back surface including a reflecting portionfacing the internal region; and an internal region disposed between thefront surface and back surface. The selectively light transmittingportion includes a side facing the internal region.

The method may further include the step of using the side of theselectively light transmitting portion facing the internal region toselectively reflect light incident from the source back through theinternal region towards the reflecting portion of the back surface.

The method may further include the step of using the reflecting portionof the back surface to reflect the light from the front surface backthrough the internal region towards the front surface.

The method may further include using the selectively light transmittingportion to selectively transmit at least a portion of light incidentfrom the reflecting portion of the back surface out of the internalregion to form the beam of light.

One or more or any part thereof of the techniques described herein canbe implemented in computer hardware or software, or a combination ofboth. The methods can be implemented in computer programs using standardprogramming techniques following the method and figures describedherein. Program code is applied to input data to perform the functionsdescribed herein and generate output information. The output informationis applied to one or more output devices such as a display monitor. Eachprogram may be implemented in a high level procedural or object orientedprogramming language to communicate with a computer system. However, theprograms can be implemented in assembly or machine language, if desired.In any case, the language can be a compiled or interpreted language.Moreover, the program can run on dedicated integrated circuitspreprogrammed for that purpose.

Each such computer program is preferably stored on a storage medium ordevice (e.g., ROM or magnetic diskette) readable by a general or specialpurpose programmable computer, for configuring and operating thecomputer when the storage media or device is read by the computer toperform the procedures described herein. The computer program can alsoreside in cache or main memory during program execution. The analysismethod can also be implemented as a computer-readable storage medium,configured with a computer program, where the storage medium soconfigured causes a computer to operate in a specific and predefinedmanner to perform the functions described herein. In some embodiments,the computer readable media is tangible and substantially non-transitoryin nature, e.g., such that the recorded information is recorded in aform other than solely as a propagating signal.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.

As used herein the term “light” and related terms (e.g. “optical”) areto be understood to include electromagnetic radiation both within andoutside of the visible spectrum, including, for example, ultraviolet andinfrared radiation.

1. An apparatus for collecting light from a source into a beam of light,said apparatus comprising: a front surface comprising a selectivelylight transmitting portion; a back surface comprising a reflectingportion; and an internal region disposed between the front surface andback surface; said selectively light transmitting portion comprising aside facing the internal region which selectively reflects lightincident from the source back through the internal region towards thereflecting portion of the back surface; said reflecting portion of theback surface reflecting the light from the front surface back throughthe internal region towards the front surface; and said selectivelylight transmitting portion selectively transmitting at least a portionof light incident from the reflecting portion of the back surface out ofthe internal region to form the beam of light.
 2. The apparatus of claim1, wherein the internal region comprises a refractive material.
 3. Theapparatus of claim 2 wherein the refractive material comprisesdielectric material.
 4. The apparatus of claim 2, wherein theselectively light transmitting portion comprises an interface betweenthe refractive material in the internal region and a material outsidethe internal region having a differing index of refraction, and whereinthe light selectively reflected from the selectively light transmittingportion is reflected due to total internal reflection.
 5. The apparatusof claim 4, wherein the material outside the internal region having adiffering index of refraction has an index of refraction which is lessthat the index of refraction of the refractive material in the internalregion.
 6. The apparatus of claim 5, wherein the material outside theinternal region comprises a fluid having an index of refraction of aboutn=1.
 7. The apparatus of claim 2, wherein the refractive material in theinternal region comprises a fluid.
 8. The apparatus of claim 7, whereinthe refractive material comprises a material selected from the listconsisting of: water, oil, mineral oil.
 9. The apparatus of claim 7,further comprising a shell surrounding the internal region, said shellcomprising the front and back surfaces.
 10. The apparatus of claim 7,further comprising a circulator for circulating the fluid through theinternal region.
 11. The apparatus of claim 10, wherein the circulatoris adapted to remove heat from the internal region.
 12. The apparatus ofclaim 2, having a focal point located in a focal plane, and wherein thesource is located proximal to the focal point, and the front and backsurfaces are configured to cooperate to collect light from the sourceand substantially collimate the light into the beam.
 13. The apparatusof claim 12, wherein the front surface and back surface are asphericalsurfaces adapted to substantially eliminate spherical and comaticaberration associated with light collected from the source locatedproximal to the focal point.
 14. The apparatus of claim 13, whereinlight rays collected from the focal point and collimated into the beamsubstantially satisfy the Abbe sine condition.
 15. The apparatus ofclaim 2, wherein the reflecting portion of the back surface comprises ametalized surface portion.
 16. The apparatus of claim 2, wherein thefront surface comprises a centrally located reflector comprising areflective side facing towards the internal region and a light blockingside facing away from the internal region; wherein the selectively lighttransmitting portion of the front surface substantially surrounds thecentrally located reflector.
 17. The apparatus of claim 16, wherein thecentrally located reflector provides a central obscuration of less thanabout 3%.
 18. The apparatus of claim 16, wherein the centrally locatedreflector provides a central obscuration of less than about 7%.
 19. Theapparatus of claim 16, wherein the centrally located reflector providesa central obscuration of less than about 10%.
 20. The apparatus of claim12, wherein the apparatus is disposed about an optical axis extendingnormal to the focal plane, and wherein light emitted from the source atangles less than 60 degrees from the optical axis are collected into thebeam.
 21. The apparatus of claim 20, wherein at least 80% of the lightpower emitted from the source is collected into the beam.
 22. Theapparatus of claim 20, wherein at least 70% of the light power emittedfrom the source is collected into the beam.
 23. The apparatus of claim12, wherein the apparatus is disposed about an optical axis extendingnormal to the focal plane, and wherein light emitted from the source atangles less than 60 degrees from the optical axis are collected into thebeam.
 24. The apparatus of claim 12, wherein the apparatus is disposedabout an optical axis extending normal to the focal plane, and whereinlight emitted from the source at angles less than 80 degrees from theoptical axis are collected into the beam.
 25. The apparatus of claim 1,having an f/number of about 1.0 or less.
 26. A method comprising:providing an apparatus for collecting light from a source into a beam oflight, said apparatus comprising: a front surface comprising aselectively light transmitting portion; a back surface comprising areflecting portion facing the internal region; and an internal regiondisposed between the front surface and back surface, said selectivelylight transmitting portion comprising a side facing the internal region;using the side selectively light transmitting portion facing theinternal region to selectively reflect light incident from the sourceback through the internal region towards the reflecting portion of theback surface; using the reflecting portion of the back surface toreflect the light from the front surface back through the internalregion towards the front surface; and using the selectively lighttransmitting portion to selectively transmit at least a portion of lightincident from the reflecting portion of the back surface out of theinternal region to form the beam of light.